On this page:

Gross anatomy

The optic tracts course posterolaterally through the ambient cistern from the chiasma to the lateral geniculate nucleus of the thalamus. Most axons synapsis with this nucleus and carry visual fibres. A smaller proportion of axons branches off medially from the optic tract to course between the medial and lateral geniculate nuclei and towards the tectal plate to synapsis with the superior colliculus. This small branch, the superior brachium, carry fibres responsible for the light reflex.